Google CEO Eric Schmidt stepped down from his post on Monday as scheduled, opening to the door for co-founder Larry Page to take the reins. But the transition comes at an awkward time for the company, which is facing antitrust complaints in the European Union (EU) and, possibly, the United States now as well.

Page promises a more aggressive Google, one that is better positioned to quickly move into new markets and react to changing market forces. But in a bad sign, Page's first day on the job was also marked by the sudden and unexpected departure of Senior VP of Product Management Jonathan Rosenberg. Mr. Rosenberg said he won't be joining another company but will instead write a book with Schmidt.

Meanwhile, since announcing the executive shuffle three months ago, Page has already worked to remove layers of Google's corporate hierarchy in a bid to help the company make quicker decisions. Sources say he's changed the structure of meetings, as well, making them more efficient.

Some might wonder why Google needs to change. After all, the company rocketed to success in its decade under Schmidt, purchasing important online services such as AdSense and YouTube and launching Gmail, Android, Chrome, and many other products during this time. And Google's core product, Internet search, is dominant, with roughly 65 percent of the market in the United States and 90 to 95 percent of the market is some European nations.

But that's part of the problem: Google's dominance has led to some antitrust scrutiny in recent days. Recent deals, including its 2007 purchase of DoubleClick, were heavily contested, as is a recent attempt to purchase ITA, the maker of widely used online travel services. Google is facing an antitrust inquiry in Europe already, and Microsoft added its weight to matters by filing a formal antitrust complaint against the company that focuses on search, advertising, and mobile software.

And now the United States might be stepping in as well. According to a report in Bloomberg, the US Federal Trade Commission is considering Google's search dominance in the United States as the target for a broad antitrust investigation. The probe could be "on par" with a similar (and epic) antitrust case against Microsoft that the US Department of Justice executed a decade ago. The results of that action hobble Microsoft to this day and led, in part, to the rise of Google during the same time period.

In fact, it is Microsoft that Google is most worried about now, though not in the way you might be thinking: Just as Microsoft before it was openly concerned about becoming the next IBM, Google is worried about becoming the next Microsoft—a too-big, too-slow company that can't innovate or lead in new markets. Page's ascendancy to CEO was designed to prevent this from happening, or at least to roll back some of the Microsoftian tendencies that came to the forefront in the past few perhaps-too-comfortable years under Schmidt.

We'll see if Page has what it takes. In the high-tech world, at least, company founders and one-time CEOs who return to the top spot at the company infrequently see much success in their second-go-round, with Apple's Steve Jobs being the obvious exception. The question is whether Page performs more like Jobs or follows in the footsteps of Gateway's Ted Waitt, Dell's Michael Dell, or Yahoo!'s Jerry Yang.